Organic semiconductor material and organic electronic device

ABSTRACT

An organic semiconductor material comprising a compound which has a generalized porphyrin skeleton and which has a molecular structure such that the distance from the generalized porphyrin ring plane to the center of each atom forming the generalized porphyrin skeleton, is not more than 1 Å.

The entire disclosures of Japanese Patent Application No. 2002-089425filed on Mar. 27, 2002, Japanese Patent Application No. 2002-104639filed on Apr. 8, 2002 and Japanese Patent Application No. 2003-049561filed on Feb. 26, 2003 including specifications, claims, drawings andsummaries are incorporated herein by reference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic semiconductor material andan organic electronic device such as a field effect transistor.Particularly, it relates to an organic semiconductor material comprisinga generalized porphyrin compound having a specific structure, and anorganic electronic device employing such a material.

2. Discussion of the Background

Heretofore, as a field effect transistor (hereinafter sometimes referredto as FET) device, one employing, as a semiconductor layer, an inorganicsemiconductor material such as a silicon (Si) or gallium arsenide singlecrystal, has been widely used. However, in the case of an inorganicmaterial, it will be treated at a high temperature of at least 300° C.at the time of its production, whereby it is difficult to employ aplastic (or resin) for the substrate, and a large energy is required forits production. It requires a production process under vacuum, such asvapor deposition, sputtering or CVD, whereby it is difficult to producea device having a large surface area. Further, it requires an expensiveinstallation in its production line, thus leading to a problem of a highcost, etc.

Under the circumstances, an organic electronic device has been proposedwherein an organic semiconductor material is used for a semiconductorlayer of an electronic device such as a field effect transistor, a lightemitting diode or a nonlinear optical device. According to such aproposal, such a semiconductor layer can be prepared by a relatively lowtemperature process, whereby a plastic film can be used as thesubstrate, and there is a merit such that a device which is light inweight, excellent in flexibility and scarcely breakable, can beprepared. Further, it can be formed by a coating method or a printingmethod, whereby there is a merit such that a device having a large areacan be produced at low cost without necessity of an expensiveinstallation. Further, the organic material is rich in variation, and itis possible to basically change the properties of the material bychanging its molecular structure, whereby there is a possibility that itis possible to obtain a device having a function which an inorganicmaterial can not provide.

Organic semiconductor materials may be classified broadly into two typesi.e. high molecular compound material (a polymer material) and lowmolecular compound material. With respect to each of them, there is areport i.e. on a device employing a conductive high molecular compoundor a conjugated high molecular compound (JP-A-61-202467), or on a deviceemploying a low molecular compound (JP2984370).

As such a high molecular compound material, a conductive polymer or aconjugated polymer is, for example, typical, and it has been attemptedto use a conjugated polymer compound as it is, as a semiconductor, or tocarry out switching by applying an electric field to introduce orwithdraw ions (dopants) to or from a conjugated polymer compound.However, there have been problems inherent to a polymer, such that thesolubility in a solvent is low, whereby a uniform coating fluid canhardly be obtained, the film is poor in uniformity or stability, defectsattributable to incomplete structural portions are likely to resultduring the film formation, the purification is difficult, and theoxidation potential tends to be low, whereby the material is susceptibleto oxidation. Thus, a material having high performance and highstability has not yet been found.

Whereas, in the case of the low molecular compound, the structure of thecompound obtainable as a result of the synthesis is substantiallypredetermined, and various purification methods such as sublimationpurification, recrystallization, column chromatography, etc. can beused. Thus, it is superior in that the purity is high, and a materialhaving high performance and high stability can readily be obtainable.

As an example of such a low molecular compound material, an aromaticcondensed hydrocarbon compound such as pentacene or an oligothiophenehaving 4 or more thiophene rings chained, which as formed into a film byvapor deposition, shows a mobility as high as amorphous silicon (a-Si),has been reported. However, such a low molecular compound tends to beoxidized although not so much as the high molecular weight compound, andthere is a problem from the viewpoint of the stability. Namely, oxygenin the air is likely to be doped to the organic semiconductor film,whereby it is likely that the carrier density increases, and the leakagecurrent increases or the mobility changes, whereby constantcharacteristics can hardly be obtainable.

Further, the low molecular compound can hardly be one whereby thecharacteristics of an organic compound are sufficiently utilized, sincea coating process is hardly applicable thereto, and it is required toemploy a film-forming method by vapor deposition which makes theproduction cost high. Further, if the low molecular weight compound isformed into a film by coating of its solution, a uniform film can hardlybe obtainable, since it will have a granular structure bycrystallization, and thus, there will be many cases wherein there is aproblem in the film forming properties.

For example, applications of phthalocyanines to field effect transistorshave been reported (JP-A-11-251601, JP-A-2000-174277, Appl. Phys. Lett.,vol. 69 (1996), p. 3,086). However, phthalocyanines are usuallyinsoluble in solvents, to prepare such devices, and it is necessary tocarry out film formation by a vacuum vapor deposition method.

Under the circumstances, methods have been reported in recent yearswherein a precursor for a low molecular compound having a highsolubility in a solvent, is dissolved in a solvent or the like, thenformed into a film by a coating process and then converted to asemiconductor to obtain an organic semiconductor film, so that a fieldeffective transistor is thereby prepared. For example, there are caseswherein pentacene or analogous aromatic hydrocarbons are employed(Science, vol. 270 (1995) p. 972, Optical Materials vol. 12 (1999), p.189, J. Appln. Phys. Vol. 79 (1996) p. 2,136).

Here, the operation characteristics of a field effect transistor aredetermined mainly by the carrier mobility μ or electroconductivity ofthe semiconductor layer, the capacitance Ci of the insulating layer, andthe construction of the device (such as the source•drain electrodedistance L and width W, the thickness d of the insulating layer, etc.).Among them, it is important that the carrier mobility μ (hereinaftersometimes referred to simply as the mobility) of the semiconductormaterial to be used for the semiconductor layer, is high. With respectto pentacene, a case where the mobility is 0.2 cm²/Vs depending upon thecondition of the film, has been reported. However, the mobilitydemonstrated by an actual application to a device has been at a level of10⁻² cm²/Vs, and the mobility in the practical use is not yet high.Further, from the pentacene precursor in this case, a tetrachlorobenzenemolecule will be detached, but tetrachlorobenzene is not only hardlyremovable from the reaction system as the boiling point is high, butalso problematic in view of its toxicity.

Meanwhile, as a material for an optical device to obtain a photoelectriccurrent or photoelectromotive force, a porphyrin compound has beenstudied, and an application of benzoporphyrin to a solar cell isdisclosed in JP-A-9-18039. However, its carrier mobility is low, andwhen the mobility is calculated from the carrier density and theresistivity disclosed in Examples, it is still at a level of 1.3×10⁻⁶cm²/Vs even at the maximum. Since the mobility is so low, the study onthe application of the porphyrin compound has been limited to an opticaldevice, and no application to an organic electronic device has beenobserved wherein all mobility or electromobility is positively utilized.

As described above, an organic semiconductor material has variouscharacteristics which are not observed with an inorganic semiconductormaterial. However, organic semiconductor materials having relativelyhigh performance, such as phthalocyanines, pentacenes oroligothiophenes, are all restricted in that the process for theirproduction has been limited to a vapor deposition process which ishighly costly. Therefore, it is desired to obtain an organic electronicdevice which can be produced by a simpler process and which, at the sametime, has practical characteristics.

Accordingly, an organic semiconductor material which has high carriermobility and stability and which can be formed into a film by a simpleproduction process such as a coating process, and an organic electronicdevice employing such an organic semiconductor material, have beendesired.

SUMMARY OF THE INVENTION

As a result of various studies made under the above circumstances, ithas been found that an organic electronic device employing, as asemiconductor material, a compound having a certain specific porphyrinskeleton, is useful, and the present invention has been accomplished onthe basis of this discovery. With respect to porphyrin, an applicationto a solar cell has been known. However, in that application, themobility has been still inadequate, probably because purification of theporphyrin itself has been inadequate. Thus, heretofore, no attention hasbeen drawn to a porphyrin compound as a material for an organicelectronic device, since its synthesis or purification has beendifficult.

However, as a result of the study on the application of a porphyrincompound by the present inventors, it has been surprisingly found that acompound having a certain specific generalized porphyrin skeleton can beformed into a film even by a solution process and shows a high mobility,and it thus presents an advantageous performance as compared with otherorganic semiconductor materials.

Namely, in a first aspect, the present invention provides an organicsemiconductor material comprising a compound which has a generalizedporphyrin skeleton and which has a molecular structure such that thedistance from the generalized porphyrin ring plane to the center of eachatom forming the generalized porphyrin skeleton, is not more than 1 Å

In a second aspect, the present invention provides an organicsemiconductor material comprising a compound which has a generalizedporphyrin skeleton and which has a mobility of at least 1×10⁻⁵cm²/Vs.

In a third aspect, the present invention provides an organic electronicdevice comprising a semiconductor layer and at least two electrodes,wherein the semiconductor layer contains the above organic semiconductormaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1D are schematic views showing field effect transistors(FET) of the present invention.

FIG. 2 is a schematic view showing a static induction transistor (SIT)of the present invention.

FIGS. 3E and 3F are schematic views showing diode devices of the presentinvention.

FIG. 4 is a graph showing the results of a thermal analysis of theporphyrin compound obtained in Preparation Example 1.

FIG. 5 is a graph showing the IR spectrum of a film obtained by drying asolution of the porphyrin compound (1) obtained in Preparation Example1.

FIG. 6 is a graph showing the IR spectrum of a film obtained by furtherheating the film of FIG. 5 obtained in Preparation Example 1.

FIG. 7 is a graph showing the thin film absorption spectra before andafter heating in Preparation Example 1.

FIG. 8 is a graph showing the results of the observation of the FETcharacteristics in Example 1.

FIG. 9 is a graph showing the X-ray diffraction patterns of thesemiconductor film in Example 5.

FIG. 10 is a graph showing the X-ray diffraction patterns of thesemiconductor films in Examples 5 and 6.

FIG. 11 is a graph showing the hysteresis of the drain current byscanning of the gate voltage, of the devices of Examples 6 and 7.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Now, preferred embodiments of the present invention will be described indetail.

Firstly, the organic semiconductor material of the present inventionwill be described. In the present invention, a compound having aspecific generalized porphyrin skeleton, is employed.

Compound having a Generalized Porphyrin Skeleton

In the present invention, the compound having a generalized porphyrinskeleton is a general term for a compound having a porphyrin skeletonand a compound having an expanded porphyrin skeleton, which is ananalogue having the number of pyrrole rings forming a porphyrin skeletonincreased or having a pyrrole ring replaced by e.g. a thiophene ring ora furan ring, and it is a concept including, for example, porphyrintype, thiaporphyrin type, dithiaporphyrin type, oxaporphyrin type,dioxaporphyrin type and thiaoxaporphyrin type compounds.

Specifically, in the present invention, the compound having ageneralized porphyrin skeleton, is a compound containing a structurerepresented by the following formula (A).

In the above formula, each of Y¹ to Y^(n) which are independent of oneanother, is a π-conjugated single ring of hydrocarbon ring orheterocyclic ring, and each of Y¹ to Y^(n) may be substituted. Each ofX¹ to X^(n) which are independent of one another, is a direct bond or aconnecting group consisting of a linear hydrocarbon group, and each ofX¹ to X^(n) may be substituted. Here, the symbol

represents a single bond or a double bond. n is an integer of from 4 to20. Further, in the structure represented by the above formula (A) as awhole, π-electron systems are conjugated in a ring form. Namely, thestructure represented by the above formula is a structure in whichπ-conjugated rings represented by Y¹ to Y^(n) are π-conjugated as awhole via X¹ to X^(n). Accordingly, each of Y¹ to Y^(n) is a planarunit, and the structure represented by the above formula (A) as a wholetakes a structure having a very high planar nature.

For an organic semiconductor material to have high carrier mobility, itis desired that adjacent molecules well overlap each other in a solidstate. Namely, for a carrier i.e. an electron or a hole to betransmitted between molecules, interaction between π-electron orbitalsis important. It is well known that in an organic semiconductor,π-electrons play an important role for charge transport. However,substantially no case is known wherein π-electrons are conjugated to amacroscopic scale to show a semiconductor characteristic.

Particularly, in a molecular crystal, conjugation of π-electrons islimited within the molecule, and charge transport is done by themovement of an electric charge between molecules. In such a case, thegreater the overlapping of π-orbitals conjugated within the molecules,the higher the efficiency of the charge transport. Therefore, themobility of the molecular crystal will also have a directionaldependency. Further, this is reflected also to the fact that usually, ahighly crystalline material shows a higher mobility than an amorphousmaterial.

In order to increase the overlapping of π-orbitals among molecules, itis desired that the planar nature of π-conjugated systems in themolecules, is high. As an index for the planar nature, the deviation ofatoms forming the generalized porphyrin skeleton, from the generalizedporphyrin ring plane, may be employed.

Accordingly, the present invention is characterized in that the distancefrom the generalized porphyrin ring plane to the center of each atomforming the generalized porphyrin skeleton, is not more than 1 Å. Ifthis distance is within 1 Å, the conditions to increase the mobility andto provide a high planar nature, can be satisfied.

Here, “a generalized porphyrin ring” means a structure represented bythe formula (A) comprising π-conjugated rings represented by Y¹ to Y^(n)and X¹ to X^(n). “The generalized porphyrin ring plane means” a planesuch that the sum of squares of the distances from the centers of allatoms forming the generalized porphyrin ring, becomes minimum. Further,“the generalized porphyrin skeleton” includes, in addition to atomsforming the generalized porphyrin ring, an atom or atomic group which isbonded to the generalized porphyrin ring and which is restrained fromfree rotation by a thermal energy at a level of room temperature (i.e.25° C.).

Here, “an atom or atomic group which is bonded to the generalizedporphyrin ring and which is restrained from free rotation by a thermalenergy at a level of room temperature” means a case where the energybarrier against internal rotation of the bond between an atom of thegeneralized porphyrin ring and an atom directly bonded thereto, islarger than the thermal energy at room temperature (usually 25° C.). Forexample, it is a case, where the energy barrier against internalrotation is at least 10 kcal/mol.

Usually, the energy required for rotation of a bond can be obtained byactual measurement, but can also be obtained by calculation by e.g. amolecular orbital method. A non-empirical molecular orbital method suchas 6-311G (dp), or a semi-empirical molecular orbital method such asMOPAC, may be employed. Each has its own merit, i.e. by thenon-empirical molecular orbital method, the precision is good, and bythe semi-empirical molecular orbital method, the calculation isrelatively simple.

In a case where two or more generalized porphyrin rings which can berotated freely each other are contained in one molecule, it is onlyrequired that the planar nature of each generalized porphyrin ring isgood, and it is not required to take such a structure that the pluralityof porphyrin skeletons contained in one molecule are in the same plane.

Now, the compound having a generalized porphyrin skeleton of the presentinvention will be described in further detail.

In the present invention, the compound having a generalized porphyrinskeleton means a compound containing a structure represented by thefollowing formula (A):

In the above formula, each of Y¹ to Y^(n) which are independent of oneanother, is a π-conjugated single ring of hydrocarbon ring orheterocyclic ring, and each of Y¹ to Y^(n) may be substituted. Each ofX¹ to X^(n) which are independent of one another, is a direct bond or aconnecting group consisting of a linear hydrocarbon group, and each ofX¹ to X^(n) may be substituted. Here, the symbol

represents a single bond or a double bond. n is an integer of from 4 to20. Further, in the structure represented by the above formula (A) as awhole, π-electron systems are conjugated in a ring form.

Preferably, n is an integer of from 4 to 10, more preferably, n is aninteger of from 4 to 6, and most preferably, n is 4. n represents thenumber of π-conjugated rings Y in the above structure, but if n is toolarge, the planar nature tends to deteriorate, the electrical propertiestend to deteriorate, and the synthesis tends to be difficult.

In the above formula (A), each of Y¹ to Y^(n) which are independent ofone another, is a π-conjugated single ring of hydrocarbon ring orheterocyclic ring group, and each of Y¹ to Y^(n) may have a substituent,but is preferably a 5- to 8-membered single ring. It is more preferablya 5- or 6-membered ring. Further preferably, it is a 5-membered ring.

Preferred specific examples for Y¹ to Y^(n) will be shown below, but Y¹to Y^(n) are not limited thereto. A 5-membered ring may, for example, bea pyrrole ring, a thiophene ring, a furan ring, a thiazole ring, adithiazole ring, an oxazole ring, an oxadiazole ring, a selenophene ringor a cyclopentadiene ring. A 6-membered ring may, for example, be abenzene ring, a pyridine ring, a pyrimidine ring, a naphthalene ring, ananthracene ring or a pyrene ring.

Each of Y¹ to Y^(n) may have a substituent. For example, each of Y¹ toY^(n) may be condensed with another hydrocarbon ring or heterocyclicring to form a condensed ring. Such another ring is preferably anaromatic ring, whereby the planar nature will be increased. Further,such another ring is preferably a 5- to 8-membered ring, more preferablya 5- or 6-membered ring.

Hereinafter, the single rings of Y¹ to Y^(n) or the condensed rings madeof Y¹ to Y^(n) and another ring, will be generally referred to as ringscontaining Y¹ to Y^(n). Each of rings containing Y¹ to Y^(n) ispreferably a single ring or a 2- to 8-condensed ring, more preferably asingle ring or a 2- to 6-condensed ring, most preferably a single ringor a 2- to 4-condensed ring. It is particularly preferred that all ringscontaining Y¹ to Y^(n) are aromatic rings, whereby the planar naturewill be increased.

A preferred example of such another ring is a π-conjugated ring such asbenzene, naphthalene, anthracene, pyridine or quinoline. The condensedring made of Y¹ to Y^(n) and another ring may specifically be, forexample, a benzopyrrole ring, a benzothiophene ring or a benzofuranring.

On the other hand, an undesirable example of such another ring istypically a bicyclo ring.

The rings containing Y¹ to Y^(n) may have substituents. The followinggroups may be mentioned as specific examples of the substituents whichthe rings containing Y¹ to Y^(n) may have:

A C₁₋₁₈ linear or branched alkyl group which may be substituted, such asa methyl group, an ethyl group, a propyl group, an isopropyl group, an-butyl group, a sec-butyl group, a tert-butyl group or a n-heptylgroup; a C₃₋₁₈ cyclic alkyl group which may be substituted, such as acyclopropyl group, a cyclpentyl group, a cyclohexyl group or anadamantyl group; a C₂₋₁₈ linear or branched alkenyl group which may besubstituted, such as a vinyl group, a propenyl group or a hexenyl group;a C₃₋₁₈ cyclic alkenyl group which may be substituted, such as acyclopentenyl group or a cyclohexenyl group; a C₂₋₁₈ linear or branchedalkynyl group which may be substituted, such as a propynyl group or ahexynyl group; a heterocyclic group which may be substituted, such as a2-thienyl group, a 2-pyridyl group, a 4-piperidyl group or a morpholinogroup; a C₆₋₁₈ aryl group which may be substituted, such as a phenylgroup, a tolyl group, a xylyl group or a mesityl group; a C₇₋₂₀ aralkylgroup which may be substituted, such as a benzyl group or a phenethylgroup; a C₁₋₁₈ linear or branched alkoxy group which may be substituted,such as a methoxy group, an ethoxy group, a n-propoxy group, anisopropoxy group, a n-butoxy group, a sec-butoxy group or a tert-butoxygroup; a C₃₋₁₈ linear or branched alkenyloxy group which may besubstituted, such as a propenyloxy group, a butenyloxy group or apentenyloxy group; and a C₁₋₁₈ linear or branched alkylthio group(mercapto group) which may be substituted, such as a methylthio group,an ethylthio group, a n-propylthio group, a n-butylthio group, asec-butylthio group or a tert-butylthio group.

Other specific examples may, for example, be a halogen atom such as afluorine atom, a chlorine atom or a bromine atom; a nitro group; anitroso group; a cyano group; an isocyano group; a cyanate group; anisocyanate group; a thiocyanate group; an isothiocyanate group; amercapto group; a hydroxy group; a hydroxyamino group; a formyl group; asulfonate group; a carboxyl group; an acyl group represented by —COR⁶,an amino group represented by —NR⁷R⁸, an acylamino group represented by—NHCOR⁹, a carbamate group represented by —NHCOOR¹⁰, a carboxylate grouprepresented by —COOR¹¹, an acyloxy group represented by —OCOR¹², acarbamoyl group represented by —CONR¹³R¹⁴, a sulfonyl group representedby —SO₂R¹⁵, a sulfamoyl group represented by —SO₂NR¹⁶R¹⁷, a sulfonategroup represented by —SO₃R¹⁸, a sulfoneamide group represented by—NHSO₂R¹⁹, and a sulfinyl group represented by —SOR²⁰. Here, each of R⁶,R⁹, R¹⁰, R¹¹, R¹², R¹⁵, R¹⁸, R¹⁹ and R²⁰ is a hydrocarbon group whichmay be substituted, or a heterocyclic group which may be substituted,and each of R⁷, R⁸, R¹³ , R¹⁴ , R¹⁶ and R¹⁷ is a hydrogen atom, ahydrocarbon group which may be substituted or a heterocyclic group whichmay be substituted.

The hydrocarbon group represented by each of R⁶ to R²⁰ is a linear orbranched alkyl group, a cyclic alkyl group, a linear or branched alkenylgroup, a cyclic alkenyl group, an aralkyl group or an aryl group. It ispreferably a C₁₋₁₈ linear or branched alkyl group such as a methylgroup, an ethyl group, a propyl group, an isopropyl group, a n-butylgroup, a sec-butyl group, a tert-butyl group or a n-heptyl group, aC₃₋₁₈ cyclic alkyl group such as a cyclopropyl group, a cyclopentylgroup, a cyclohexyl group or an adamantyl group, a C₂₋₁₈ linear orbranched alkenyl group such as a vinyl group, a propenyl group or ahexenyl group, a C₃₋₁₈ cyclic alkenyl group such as a cyclopentenylgroup or a cyclohexenyl group, a C₇₋₂₀ aralkyl group such as a benzylgroup or a phenethyl group, or a C₆₋₁₈ aryl group such as a phenylgroup, a tolyl group, a xylyl group or a mesityl group. The aryl groupmoiety of such a group may further be substituted by the samesubstituent as for the above-described rings containing Y¹ to Y^(n).

The heterocyclic group represented by each of R⁶ to R²⁰ may, forexample, be a saturated heterocyclic group such as a 4-piperidyl group,a morpholino group, a 2-morpholinyl group or a piperazyl group, or anaromatic heterocyclic group such as a 2-furyl group, a 2-pyridyl group,a 2-thiazolyl group or a 2-quinolyl group. Such a group may contain aplurality of hetero atoms and may further have a substituent at anyposition. One having a preferred structure as the heterocyclic ring, isa 5- or 6-membered saturated heterocyclic ring or an aromaticheterocyclic ring which is a 5- or 6-membered single ring or a condensedring composed of two such 5- or 6-membered rings.

The linear or branched alkyl group, the cyclic alkyl group, the linearor branched alkenyl group, the cyclic alkenyl group, the linear orbranched alkynyl group, the linear or branched alkoxy group, or thelinear or branched alkylthio group, which the above-mentioned ringscontaining Y¹ to Y^(n) may have, and the alkyl chain moiety of the alkylgroup represented by each of R⁶ to R²⁰, may further have a substituent,and such a substituent may, for example, be as follows. A C₁₋₁₀ alkoxygroup such as a methoxy group, an ethoxy group, a n-propoxy group, anisopropoxy group, a n-butoxy group, a sec-butoxy group or a tert-butoxygroup; a C₂₋₁₂ alkoxyalkoxy group such as a methoxymethoxy group, anethoxymethoxy group, a propoxymethoxy group, an ethoxyethoxy group, apropoxyethoxy group or a methoxybutoxy group; a C₃₋₁₅ alkoxyalkoxyalkoxygroup such as a methoxymethoxymethoxy group, a methoxymethoxyethoxygroup, a methoxyethoxymethoxy group, a methoxymethoxyethoxy group or anethoxyethoxymethoxy group; a C₆₋₁₂ aryl group such as a phenyl group, atolyl group or a xylyl group (which may be further substituted by anoptional substituent); a C₆₋₁₂ aryloxy group such as a phenoxy group, atolyloxy group, a xylyloxy group or a naphthyloxy group; and a C₂₋₁₂alkenyloxy group such as an allyloxy group or a vinyloxy group.

Further, other substituents may, for example, be a heterocyclic groupsuch as a 2-thienyl group, a 2-pyridyl group, a 4-piperidyl group or amorpholino group; a cyano group; a nitro group; a hydroxyl group; anamino group; a C₁₋₁₀ alkylamino group such as an N,N-dimethylamino groupor an N,N-diethylamino group; a C₁₋₆ alkylsulfonylamino group such as amethylsulfonylamino group, an ethylsulfonylamino group or an-propylsulfonylamino group; a halogen atom such as a fluorine atom, achlorine atom or a bromine atom; a C₂₋₇ alkoxycarbonyl group such as acarboxyl group, a methoxycarbonyl group, an ethoxycarbonyl group, an-propoxycarbonyl group, an isopropoxycarbonyl group or an-butoxycarbonyl group; a C₂₋₇ alkylcarbonyloxy group such as amethylcarbonyloxy group, an ethylcarbonyloxy group, an-propylcarbonyloxy group, an isopropylcarbonyloxy group or an-butylcarbonyloxy group; and a C₂₋₇ alkoxycarbonyloxy group such as amethoxycarbonyloxy group, an ethoxycarbonyloxy group, an-propoxycarbonyloxy group, an isopropoxycarbonyloxy group or an-butoxycarbonyloxy group.

Preferred among the substituents which the rings containing Y¹ to Y^(n)may have, may, for example, be a hydroxyl group, a C₁₋₁₀ alkyl, alkoxy,mercapto or acyl group, which may be substituted, a carboxyl group orits ester with a C₁₋₁₀ alcohol, a formyl group, a carbamoyl group, ahalogen atom such as fluorine, chlorine, bromine or iodine, an aminogroup which may be substituted by a C₁₋₁₀ alkyl group, or a nitro group.Such a preferred group may further have a substituent. For example, analkyl moiety of such a substituent may further be substituted by asingle atom such as a halogen atom.

Most preferably, each of rings containing Y¹ to Y^(n) is unsubstitutedor has a substituent composed of a single atom such as a halogen atom.

Each of X¹ to X^(n) which are independent of one another, is a directbond or a connecting group consisting of a linear hydrocarbon group, andeach of X¹ to X^(n) may be substituted. The linear hydrocarbon group ispreferably one having from 1 to 10 carbon atoms, more preferably from 1to 5 carbon atoms. More preferably, it is a C₁₋₃ unsaturated linearhydrocarbon group, particularly preferably, an alkenylene group, analkynylene group, an alkanediylidene group or an alkenediylidene group.

Preferred specific examples for X¹ to X^(n) include a methine group, avinylene group (an ethenylene group), an ethynylene group and (═C═C═),but are not limited thereto. Further, each may have a substituent,although such a substituent is omitted in the above examples.

Specific examples of the substituents which X¹ to X^(n) may have, may beroughly the same as the substituents which the rings containing Y¹ toY^(n) may have. However, bulky substituents which hinder free rotation,are undesirable. Preferred substituents may be a linear alkyl groupwhich may be substituted, a linear alkoxy group, a linear mercaptogroup, an ester of a carboxyl group with a C₁₋₁₀ alcohol, or a halogenatom. The substituents which X¹ to X^(n) may have, may be bonded to eachother to form a ring.

Particularly preferred among them may be an unsubstituted linear alkylgroup, a linear alkoxy group, a linear alkylthio group, an ester of acarboxyl group with a C₁₋₁₀ linear alcohol, or a halogen atom.

Most preferably, X¹ to X^(n) are unsubstituted or have a substituentcomposed of a single atom such as a halogen atom.

On the other hand, a typical example of an undesirable substituent is aphenyl group.

Further, in the structure represented by the formula (A) as a whole, itis necessary that π-electron systems are conjugated in a ring form.

Further, the compound having a generalized porphyrin skeleton of thepresent invention, may have various metals, cations, anions, salts,etc., coordinated to some or all of Y¹ to Y^(n) in the above structure.For example, a bivalent metal atom may be mentioned, and specificexamples include Zn, Cu, Fe, Ni and Co. Further, an atomic group havinga trivalent or higher valent metal and another atom bonded, such asFe—B¹, Al—B², Ti═O or Si—B³B⁴, may, for example, be mentioned. Here,each of B¹, B², B³ and B⁴ is a monovalent group such as a halogen atom,an alkyl group or an alkoxy group.

Examples of such porphyrin type and expanded porphyrin type compoundsare disclosed, for example, in THE PORPHYRIN HANDBOOK, VOL. 1–10,ACADEMIC PRESS (2000), edited by KARL M. KADISH KEVIN, M. SMITH ROGERGUILARD.

Further, it may be one wherein the same or different two generalizedporphyrin rings are commonly conjugated to one atom, one wherein thesame or different two generalized porphyrin rings are bonded via atleast one atom or atomic group, or one wherein the same or different atleast three generalized porphyrin rings are bonded in the form of a longchain.

As the compound having a generalized porphyrin skeleton of the presentinvention, most preferred is specifically one containing a structurerepresented by the following formula (1) or (2).

In the above formulae (1) and (2), each of Z^(ia) and Z^(ib) (i=1 to 4)represents a monovalent organic group, and Z^(ia) and Z^(ib) may bebonded to form a ring. The monovalent organic group may, for example, bea hydrogen atom, a hydroxyl group, a C₁₋₁₀ alkyl group which may besubstituted, an alkoxy group, a mercapto group, an acyl group, acarboxyl group or its ester with a C₁₋₁₀ alcohol, a formyl group, acarbamoyl group, a halogen atom such as fluorine, chlorine, bromine oriodine, an amino group which may be substituted by a C₁₋₁₀ alkyl group,or a nitro group, and such a group may further have a substituent.Further, as an example of the organic group wherein Z^(ia) and Z^(ib)are bonded to form a ring, the ring formed by the structureZ^(ia)—CH═CH—Z^(ib), may, for example, be an aromatic hydrocarbon suchas a benzene ring, a naphthalene ring or an anthracene ring, aheterocyclic ring such as a pyridine ring, a quinoline ring, a furanring or a thiophene ring, or a non-aromatic cyclic hydrocarbon such as acyclohexene. Further, each of R¹ to R⁴ is a hydrogen atom or amonovalent organic group. Such an organic group may, for example, be analkyl group which may be substituted, an aryl group, an alkoxy group, amercapto group, an ester of a carboxyl group with a C₁₋₁₀ alcohol, or ahalogen atom.

Further, M is a bivalent metal atom, such as Zn, Cu, Fe, Ni or Co, or anatomic group having a trivalent or higher valent metal and another atombonded, such as Fe—B¹, Al—B², Ti═O or Si—B³B⁴. Here, each of B¹, B², B³and B⁴ is a monovalent group such as a halogen atom, an alkyl group oran alkoxy group.

Further, there may be one wherein two porphyrin rings are commonlycoordinated to one atom, one wherein two porphyrin rings are bonded viaat least one atom or atomic group, or one wherein at least three suchporphyrin rings are bonded in the form of a long chain.

As mentioned above, in order to increase overlapping of the π-orbitalsbetween molecules, the porphyrin compound of the present invention ispreferably one wherein the planar nature of the π-conjugated systems inthe molecule is high, and it is characterized in that it has a molecularstructure wherein the distance from the porphyrin ring plane to thecenter of each atom forming the porphyrin skeleton, is not more than 1Å. The atoms forming the porphyrin skeleton include, in addition toatoms forming the porphyrin ring, an atom or atomic group which isbonded to a substituent Z^(ia), Z^(ib) or R¹ to R⁴ of (1) or (2), andfree rotation of which by a thermal energy at a level of roomtemperature is restrained.

For example, carbon atoms forming four benzene rings or atetraphenylporphyrin having the benzene rings bonded at four mesopositions of a porphyrin ring, are restrained from free rotation due tosteric hindrance between the benzene rings and the porphyrin ring, andthus, they are included in the porphyrin skeleton. It is not desirablethat such groups are present at positions deviated from the plane of theporphyrin ring, since they tend to hinder overlapping of porphyrin ringsby the steric hindrance. On the other hand, in a case where rotation ofthe bond is free as in the case of an alkyl group or an alkoxy group,especially a linear alkyl group or a linear alkoxy group, the structurecan freely be adjusted so that the porphyrin rings can be overlapped,and such a group will not be a hindrance and therefore is not includedin the porphyrin skeleton.

The porphyrin ring plane can be defined as such a plane that the sum ofsquares of the distances from the centers of all atoms forming theporphyrin ring, would be minimum. If the distance from this plane to thecenters of atoms forming the porphyrin skeleton, is within 1 Å, it ispossible to satisfy the conditions that the planar nature is high, andthe mobility is high.

As typical examples of the generalized porphyrin compound not having ahigh planar nature, the following tetraphenylporphyrin, which is mostwell known as a porphyrin, and a porphyrin including bicyclo structuremay be mentioned.

Accordingly, Z^(ia) or Z^(ib) in the above formula (1) or (2) ispreferably a single atom such as a hydrogen atom or a halogen atom.Further, it may also be preferably a group forming a ring having a highplanar nature and having no substituent, particularly one wherein atleast one of Z^(ia)—CH═CH—Z^(ib) (i=1 to 4) is a group forming anaromatic ring such as benzene, naphthalene or anthracene, or one whereinall of Z^(ia)—CH═CH—Z^(ib) (i=1 to 4) are aromatic rings. Further, eachof R¹ to R⁴ is preferably a single atom such as a hydrogen atom or ahalogen atom.

In the present invention, the organic semiconductor material is alsocharacterized in that it comprises a compound which has a generalizedporphyrin skeleton and which has a carrier mobility (mobility: μ) of atleast 1×10⁻⁵ cm²/Vs.

The carrier mobility required for application to an electronic device isdetermined from the degree of the electric current to be controlled, theswitching speed and the structure of the device. By using thegeneralized porphyrin compound of the present invention, it is possibleto provide an organic device having a carrier mobility of at least1×10⁻⁵ cm²/Vs, preferably at least 1×10⁻³ cm²/Vs. The mobility of aconventional organic semiconductor of molecular crystal is at a level ofabout 1 cm²/Vs with a single crystal of an aromatic condensedhydrocarbon such as pentacene. A porphyrin molecule has π-orbitals whichare substantially expanded, whereby there is a possibility that theinteraction between molecules can be increased, and further, a centermetal is present, whereby it can be expected to utilize the interactionvia the metal, and thus it is considered possible to accomplish amobility of from 10 cm²/Vs to 100 cm²/Vs.

The purity of the semiconductor material constituting the semiconductorlayer may be mentioned as another condition for the high mobility. Animpurity which traps the carrier causes a substantial deterioration ofthe mobility even in a trace amount. An impurity which is likely to formsuch a trap, is one having a level to receive the carrier in the energygap of the semiconductor. When the carrier is a hole, it is one havingthe highest occupied molecular orbital (HOMO) level higher than thesemiconductor, and when the carrier is an electron, it is one having thelowest unoccupied molecular orbital (LUMO) level lower than thesemiconductor.

Even an impurity which presents no such an energy level, will cause adeterioration of the mobility, if the concentration becomes high tobring about a defect in the crystal structure of the semiconductor.Accordingly, the concentration of impurities is desired to be low,preferably at most 10%, more preferably at most 1%. The process ofemploying a precursor having a high solubility, which will be describedhereinafter, has a merit in that it is thereby possible to form asemiconductor layer of high purity.

With a generalized porphyrin compound, a hole will usually be a carrier,but an electron may be made to be a carrier, as electron transportproperties are provided by a substituent or by the center metal.

In a case where injection of electric charge from an electrode isrequired to take place smoothly as in the case of a field effecttransistor, a preferred position is present for the energy level of thecarrier. In the case of a hole, if HOMO is too low, the barrier againstinjection of the electric charge tends to be substantial, such beingundesirable. On the other hand, if HOMO is too high, the material tendsto be susceptible to oxidation by the air and tends to be unstable.Accordingly, the ionization potential in the solid state correspondingto the HOMO level is preferably at most 5.6 eV, more preferably at most5.3 eV. Further, the ionization potential is preferably at least 4.5 eV,more preferably at least 4.8 eV.

The compound having a generalized porphyrin skeleton of the presentinvention is preferably in a solid state at room temperature forapplication to a device. Depending upon the substituent in the formula(1) or (2), a compound showing a liquid crystal property can beobtained, and it can be used as an organic semiconductor even in aliquid crystal state. Especially, the generalized porphyrin compound ofthe present invention has a structure having a good planar nature,whereby it is expected that a discotic liquid crystal may be obtained,and such a structure is suitable for transport of a carrier. It is notdesirable that a substantial change in the properties will take placewithin the operational temperature range. Accordingly, a compound ispreferred, of which the phase transfer temperature such as a meltingpoint or a solidification point is not within a range of from 5° C. to40° C. The compound which is in a solid state at room temperature ispreferably such that the melting point or the glass transition point isat least 50° C., more preferably at least 100° C.

Further, the ON/OFF ratio of the organic semiconductor materialcomprising the generalized porphyrin compound of the present inventionis desirably as high as possible, preferably at least 800, morepreferably at least 1,000.

Now, examples of preferred generalized porphyrin compounds of thepresent invention will be given. Here, structures containing no metalare exemplified. However, metal salts corresponding to the followingexamples or the corresponding molecules having substituents may likewisebe used as preferred examples. Further, molecular structures having goodsymmetry are mainly exemplified, but asymmetrical structures by acombination of partial structures, can also be used. The porphyrincompounds of the present invention are, of course, not limited to theseexemplified compounds.

Synthesis of the Generalized Porphyrin Compound

The generalized porphyrin compound of the present invention can besynthesized by using the corresponding pyrrole compound, thiophenecompound, furan compound or the like, as the starting material. For thesynthesis of the generalized porphyrin compound, a method disclosed inTHE PORPHYRIN HANDBOOK, VOL. 1, ACADEMIC PRESS (2000), edited by KARL M.KADIS H KEVIN M. SMITH ROGER GUILARD, may, for example, be used.

For example, condensation of pyrrole and an aldehyde, is frequently usedparticularly as a synthesis of a tetraphenylporphyrin.

In the above formula, Q¹ and Q² correspond to Z^(ia) and Z^(ib) in theformula (1) or (2), and Q³ corresponds to R¹ to R⁴.

Further, it can be obtained also by a condensation reaction of a pyrrolehaving a carboxylate or a methyl group at the α-position.

In the above formulae, Q¹ and Q² correspond to Z^(ia) and Z^(ib) in theformula (1) or (2), and R⁵ is an alkyl group.

Among generalized porphyrin compounds of the present invention, abenzoporphyrin having a benzene ring condensed to at least one pyrrolering, thiophene ring or furan ring, can be prepared by using as itsprecursor, the corresponding bicyclo compound. Such a precursor is notof a planar structure, and thus, it has a high solubility in a solventand is hardly crystallizable and thus can be coated from a solution topresent an amorphous or substantially amorphous good film. This film maybe heat-treated for ethylene removal reaction to obtain a generalizedbenzoporphyrin film having a high planar nature. In the case of a nonsubstituted non-metal structure, the reaction may be represented by thefollowing chemical reaction. This reaction proceeds quantitatively byheating at a temperature of at least 100° C., preferably at least 150°C. Further, what is detached is an ethylene molecule, which willscarcely remain in the system, so that there will be no problem from theviewpoint of the toxicity or safety. Now, an example of atetrabenzoporphyrin having four benzene rings condensed, will be shown.

The following route may, for example, be mentioned as a synthesis ofthis bicyclo compound.

Here, the synthesis route up to the preparation of the pyrroleintermediate, may be replaced by another route, as follows.

A metal complex of this precursor can be obtained by mixing thiscompound with a metal salt in an organic solvent capable of dissolvingthem. The metal salt may be any salt so long as it is soluble in theorganic solvent, but an acetate is a typical example. The solvent may beany solvent so long as it is capable of dissolving the metal salt andthe bicyclo compound, but a preferred example may be chloroform, analcohol, dimethylformamide, tetrahydrofuran, acetonitrile,N-methylpyrrolidone, or a solvent mixture thereof.

Types of Devices

(1) Definition of Electronic Device

The electronic device of the present invention is a device having atleast two electrodes and designed to control the electric currentflowing between the electrodes or the resulting voltage by other thanlight, for example by electricity, magnetism or chemical substance. Itmay, for example, be a device for controlling an electric current orvoltage by an application of a voltage, a device for controlling avoltage or electric current by an application of a magnetic field, or adevice for controlling a voltage or electric current by the action of achemical substance. Such control may, for example, be rectification,switching, amplification or oscillation. The corresponding devicespresently practically realized by silicon or the like, include aresistor, a rectifier (a diode), a switching device (a transistor or athyristor), an amplification device (a transistor), a memory device, achemical sensor, and a combination of these devices, and an integrateddevice. The generalized porphyrin compound of the present invention hasa high carrier mobility μ, whereby it is highly effective when appliedto a switching device (a transistor or a thyristor).

Further, even a device to be controlled by light or to control emissionof light may be included for an application other than an operation inwhich the generalized porphyrin material directly absorbs light or emitslight, for example a device to be used for wiring or for control of theabove voltage or electric current.

More specific examples of the electronic device may be those disclosedin Physics of Semiconductor Devices, 2nd Edition (Wiley-Interscience1981) edited by S. M. Sze.

(2) Field Effect Transistor

As an example of an organic device of the present invention, a fieldeffect transistor (FET) may be mentioned. This comprises two electrodes(a source electrode and a drain electrode) in contact with thesemiconductor, and an electric current flowing between the electrodes(so-called a channel), is controlled by a voltage applied to anotherelectrode so called a gate. The gate electrode is constructed merely toapply an electric field to the semiconductor layer, whereby an electriccurrent will not basically flow, and it is called a field effecttransistor.

According to the present invention, the organic semiconductor materialis employed, and accordingly, it can be prepared by a process at arelatively low temperature, whereby a plastic film may be used as thesubstrate, and there is a merit in that a device which is light inweight, excellent in flexibility and scarcely breakable, can beprepared. Thus, it is possible to produce a field effect transistorhaving a thin film and being flexible, and such a transistor is used fora switching device for each cell, whereby an active matrix liquidcrystal display having flexibility can be prepared, and thus it iswidely applicable.

The operation characteristics of the field effect transistor aredetermined by e.g. the carrier mobility μ, the electroconductivity σ ofthe semiconductor layer, the capacitance Ci of the insulating layer, thestructure of the device (the distance L and the width W between thesource and drain electrodes, the thickness d of the insulating layer).As the semiconductor material to be used for the field effecttransistor, the higher the carrier mobility μ, the better. However, thegeneralized porphyrin compound of the present invention has acharacteristic that the carrier mobility μ is high, whereby when it isused for the field effect transistor, it is highly effective. Further,the field effect transistor of the present invention has a small leakcurrent, and the ON/OFF ratio is large, whereby there is a merit thatthe stability of the film and the properties is high, and the usefullife is long. Further, there are merits such that the useful temperaturewidth is wide, the film forming property is good, it can be applicableto a large area, and it can be produced at low cost.

It is common to employ a structure wherein the gate electrode isinsulated by an insulating film (Metal-Insulator-Semiconductor i.e. MISstructure). Further, there is a structure wherein a gate electrode isformed via a Schottkey barrier. However, in the case of FET employing anorganic semiconductor material, the MIS structure is commonly employed.

Now, the field effect transistor of the present invention will bedescribed in further detail with reference to the drawings, but thepresent invention is by no means restricted to such structures.

In FIGS. 1A to 1D, some structural examples of the field effecttransistor device are shown. Reference numeral 1 represents asemiconductor layer, 2 an insulator layer, 3 and 4 a source electrodeand a drain electrode, 5 a gate electrode, and 6 a substrate. Thedisposition of the respective layers and electrodes can be suitablyselected depending upon the application of the device. As the electriccurrent flows in a direction parallel to the substrate, the device iscalled a horizontal FET.

The substrate 6 is required to be such that each layer formed thereoncan be maintained without peeling. As such a material, an insulatingmaterial, such as a sheet or film made of a resin, paper, glass orceramics, one having an insulating layer formed by coating or the likeon a conductive substrate made of a metal or an alloy, a compositematerial made of a combination of various types such as a resin and aninorganic material, may, for example, be mentioned. It is preferred toemploy a resin film or paper, since flexibility can be imparted to thedevice.

A material having an electrical conductivity is used for the electrodes3, 4 and 5. For example, a metal such as platinum, gold, aluminum,chromium, nickel, cobalt, copper, titanium, magnesium, calcium, bariumor sodium, or an alloy containing them, an electroconductive oxide suchas InO₂, SnO₂ or ITO, an electroconductive polymer compound such aspolyaniline, polypyrrole, polythiophene, polyacetylene orpolydiacetylene, a semiconductor such as silicon, germanium or galliumarsenide, or carbon material such as carbon black, fullerene, carbonnanotube or graphite, may, for example, be mentioned. Further, dopingmay be applied to the electroconductive polymer compound or to asemiconductor. The dopant may, for example, be an acid such ashydrochloric acid, sulfuric acid or sulfonic acid, a Lewis acid such asPF₆, AsF₅ or FeCl₃, a halogen atom such as iodine, or a metal atom suchas sodium or potassium. Further, a conductive composite material havingcarbon black or metal particles dispersed to the above material, mayalso be employed.

Further, to the electrodes 3, 4 and 5, wirings not shown, are connected,and such wirings may be made of substantially the same materials as theelectrodes.

For the insulating layer 2, a material having an insulating property canbe employed. For example, a polymer such as polymethyl methacrylate,polystyrene, polyvinylphenol, polyimide, polycarbonate, polyester,polyvinyl alcohol, polyvinyl acetate, polyurethane, polysulfone, anepoxy resin or a phenol resin, a copolymer prepared by a combinationthereof, an oxide such as silicon dioxide, aluminum oxide or titaniumoxide, a ferroelectric oxide such as SrTiO₃ or BaTiO₃, a nitride such assilicon nitride, a dielectric such as a sulfide or fluoride, or apolymer having such dielectric particles dispersed therein, may bementioned.

As mentioned above, the thickness of the insulating layer 2 ispreferably as thin as possible within a range where the necessaryfunctions can be obtained. Usually, the thickness is at least 1 nm,preferably at least 5 nm, more preferably at least 10 nm. However,usually, the thickness is at most 10 μm, preferably at most 1 μm, morepreferably at most 500 nm.

With respect to the material of the semiconductor layer 1, asemiconductor layer containing the above-mentioned generalized porphyrincompound as the main component, is preferably employed. The maincomponent means that it is contained in an amount of at least 50 wt %.More preferably, it is contained at least 80 wt %. In order to improvethe properties or to impart other properties, other organicsemiconductor materials may be mixed, or various additives may be added,as the case requires. Further, the semiconductor layer 1 may be composedof a plurality of layers.

The thickness of the semiconductor layer 1 is preferably as thin aspossible within a range where the necessary functions can be obtained.In a horizontal field effect transistor device (a source electrode and adrain electrode as disposed substantially horizontally) as shown in FIG.1, the characteristics of the device are not dependent on the filmthickness so long as the film thickness is at least a prescribed level.On the other hand, if the film thickness becomes thick, a leak currenttends to increase. In order to obtain the necessary functions, the filmthickness is usually at least 1 nm, preferably at least 5 nm, morepreferably at least 10 nm. However, the film thickness is usually atmost 10 μm, preferably at most 1 μm, more preferably at most 500 nm.

In an organic electronic device of the present invention, between therespective layers, or on the outer surface of the device, another layermay be provided, as the case requires. For example, a protective layermay be formed on the semiconductor layer directly or via another layer,whereby there will be a merit such that the influence of the outeratmosphere such as moisture can be minimized. Further, there is a meritthat the electrical characteristics can be stabilized, such that theON/OFF ratio of the device is increased.

The material for the protective layer is not particularly limited. Forexample, films made of various resins such as an epoxy resin, an acrylicresin such as polymethyl methacrylate, polyurethane, polyimide,polyvinyl alcohol, a fluorinated resin and polyolefin, or films made ofdielectrics, such as inorganic oxide films or nitride films, of e.g.silicon oxide, aluminum oxide, or silicon nitride, may preferably bementioned. Particularly, a resin (polymer) having low water absorptivityor low permeability of oxygen or moisture, is preferred.

Some of generalized porphyrin compounds may absorb light to generate anelectric charge. If necessary, the electronic device portion may beshielded from light, for example, by forming a pattern (a so-calledblack matrix) having a low light transmittance at a desired region. Forsuch a pattern, a film of a metal such as chromium, aluminum, silver orgold, a resin film having a pigment such as carbon black dispersedtherein, or a film of an organic dye, may, for example, be used.

(3) Static Induction Transistor (SIT)

A static induction transistor (SIT) may be mentioned as one type of thefield effect transistor. The structure of SIT will be described.

In horizontal FET, a source electrode and a drain electrode are disposedon a substrate, and the current flowing direction is perpendicular tothe electric field induced by the gate. Whereas, SIT is characterized inthat at a proper position between a source electrode and a drainelectrode, a gate electrode is disposed in a grid pattern, and thecurrent flowing direction is in parallel with the electric field inducedby the gate.

FIG. 2 is a schematic view showing a static induction transistor (SIT).Reference numeral 7 represents a source electrode, 8 a drain electrode,9 a gate electrode, and 10 a semiconductor layer. These are formed on asubstrate not shown. According to this SIT structure, the flow ofcarriers will spread in a plane, whereby a large amount of carriers canbe moved all at once. Further, the source electrode and the drainelectrode are arranged vertically, whereby the electrode spacing can beminimized, and the response speed will be high. Accordingly, thisstructure can be preferably applied to an application where a largecurrent is conducted or switching is carried out at a high speed.

With respect to the semiconductor layer 10, the same description as ofthe above semiconductor layer 1 applies, and with respect to theelectrodes 7 and 8, the same description as of the above electrodes 3, 4and 5 applies.

The gate electrode 9 has a network or stripe structure, so that carrierswill pass through spacings of the network or stripe structure. Thespacings of the network of the gate electrode are preferably smallerthan the distance between the source and the drain (which corresponds tothe thickness of the device). Further, the thickness of the electrode isusually at least 10 nm, preferably at least 20 nm. However, it isusually at most 10 μm, preferably at most 1 μm.

As the material for the gate electrode 9, the same material as for theabove-mentioned electrodes 3, 4 and 5 may be employed. However,preferably, an insular structured thin film made of a conductivematerial such as a metal, alloy or conductive polymer, is employed. Forexample, a semitransparent aluminum electrode in the form of a thin filmhaving a thickness of at most 50 nm may be employed.

Between the gate electrode 9 and the semiconductor layer 10, it iscommon to provide an insulating layer or an energy barrier to preventoutgoing or incoming of carriers to or from the electrode. For example,an insulating layer may be formed by patterning around the electrode.Otherwise, as the electrode material, a metal capable of forming anenergy barrier against a semiconductor may be selected to suppressoutgoing or incoming of carriers to or from the semiconductor layer. Forexample, by selecting aluminum, a so-called shot key barrier can beformed against a p-type semiconductor.

Further, between the respective layers or on the outer surface of thedevice, another layer may be formed as the case requires.

The static induction transistor of the present invention has such meritsthat the carrier mobility u is high, the leak current is small, theON/OFF ratio is large, the stability of the film and the properties ishigh, and the useful life is long. Further, it has such merits that theuseful temperature range is wide, the film forming property is good, itis applicable to a large area, and it can be produced at low cost.

(4) Diode Device

As another example, a diode device may be mentioned. This is atwo-terminal device having an asymmetrical structure. FIGS. 3E and 3Fare schematic views of diode devices. These devices are provided onsubstrates not shown.

The device of 3E has a structure wherein a semiconductor layer 13comprising the generalized porphyrin compound is sandwiched between twometal electrodes 11 and 12 having different work functions. With respectto the semiconductor layer 13, the same description as of the abovesemiconductor layer 1 applies. At least one of the electrodes 11 and 12forms an energy barrier against the semiconductor material. To form theenergy barrier, the electrodes and the semiconductor may be selected tohave different work functions. For example, as a metal to form an energybarrier against the p-type semiconductor, aluminum is often used. Asother electrode materials, the same ones as for the above-describedelectrodes 3, 4 and 5 may be employed, but preferred is a metal or analloy. When a voltage is applied to this device, so-called rectificationwill be observed, wherein the flowing current value varies dependingupon the polarity of the voltage. Accordingly, as an application of sucha diode device, a rectification device may be mentioned.

Whereas, the device shown in FIG. 3F has a structure in whichsemiconductor layers 16 and 17 having substantially different workfunctions, are sandwiched between electrodes 14 and 15. With respect tothe semiconductor layer 16, the same description as of the abovesemiconductor layer 1 applies. The semiconductor layer 17 may be made ofany material so long as its work function is substantially differentfrom the semiconductor layer 16, and as such a material, a perylenepigment, a phthalocyanine material, fullerene or a conjugated polymer,may, for example, be mentioned. With respect to the electrodes 14 and15, they may be made of the same material or different materials. Thesame materials as for the above electrodes 3, 4 and 5 may be employed.

Further, between the respective layers or on the outer surface of thedevice, another layer may be provided as the case requires.

(5) Resistance, etc.

Further, as another application, a resistant element may be mentioned.This is a two-terminal element having a symmetrical structure in which asemiconductor layer formed on a substrate is sandwiched between twoelectrodes. The resistant element may be used as a resistor to adjustthe resistance between the electrodes, or as a capacitor to adjust thecapacitance between the electrodes by increasing the resistance.

With respect to the semiconductor layer, the same description as of theabove semiconductor layer 1 applies, and with respect to the electrodes,the same description as of the above electrodes 3, 4 and 5 applies.

Further, between the respective layers or on the outer surface of theelement, another layer may be provided, as the case requires.

Such a diode device or the resistance element will have a merit suchthat by using the organic semiconductor material of the presentinvention showing a high carrier mobility, the device parameter such asthe resistance value can be controlled widely, such is advantageous forintegration.

(6) Application of the Organic Electronic Device of the PresentInvention

(6-1) Active Matrix

The organic electronic device of the present invention can be used as aswitching device of an active matrix of a display. Namely, by utilizingthe ability to switch the electric current between the source and thedrain by the voltage applied to the gate, the switch is put on only whena voltage is applied or a current is supplied to a display device, andduring other time, the circuit is open, thereby to carry out high speedhigh contrast display.

As a display device to which the present invention is applicable, aliquid display device, a polymer-dispersed type liquid crystal displaydevice, an electrophoretic display device, an electroluminescent deviceor an electrocromic device may, for example, be mentioned.

Particularly, with the organic electronic device of the presentinvention, preparation of the device by a low temperature process ispossible, and it is possible to employ a substrate which is not durableagainst high temperature treatment, such as a plastic plate, a plasticfilm or paper. Further, preparation of the device by a coating orprinting process is possible, it is suitable for application to adisplay having a large area. Further, it is advantageous as a devicewhich makes an energy saving process or a low cost process possible, oras a substitute for a conventional active matrix.

(6-2) IC

Further, by integrating a transistor, a digital device or an analoguedevice can be realized. As such an example, a logical circuit such asAND, OR, NAND or NOT, a memory device, an oscillation device or anamplification device may, for example, be mentioned. Further, by acombination thereof, an IC card or an IC tag may be prepared.

(6-3) Sensor

An organic semiconductor undergoes a substantial change in itsproperties by an external stimulus such as a gas, a chemical substanceor a temperature, and its application to a sensor is conceivable. Forexample, by measuring the amount of change in the properties of theorganic electronic device of the present invention by its contact with agas or a liquid, it is possible to detect chemical substances containedtherein quantitatively or qualitatively.

Process for Producing the Organic Electronic Device of the PresentInvention

A preferred process for producing the organic electronic device of thepresent invention will be described with reference to a case of thefield effect transistor (FET) shown in FIG. 1A, but such a process islikewise applicable to other organic electronic devices.

(1) Substrate and Treatment of the Substrate

In general, an organic electronic device such as a field effecttransistor is prepared by providing a necessary layer and electrodes ona substrate 1. As the substrate, one described above can be employed.

In some cases, it is possible to improve the properties of the device byapplying a prescribed surface treatment to the substrate. For example,by adjusting the degree of hydrophilicity/hydrophobicity of thesubstrate surface, the quality of the film to be formed thereon can beimproved. Especially, the properties of the organic semiconductormaterial will change substantially by the state of the film such asalignment of molecules, and by surface treatment of the substrate, it isconsidered possible to control the molecular alignment at theinterfacial portion between the substrate and the semiconductor film tobe formed thereon, thereby to improve the properties.

Such treatment of the substrate may, for example, be hydrophobictreatment with e.g. hexamethyldisilazane, cyclohexene or octadecyltrichlorosilane, acid treatment with e.g. hydrochloric acid, sulfuricacid or acetic acid, alkali treatment with e.g. sodium hydroxide,potassium hydroxide, calcium hydroxide or ammonia, ozone treatment,fluorination treatment, plasma treatment in e.g. oxygen or argon,treatment for forming a Langmuir•Blodgett film, treatment for forming athin film of other insulator or semiconductor, mechanical treatment, orelectric treatment such as corona discharge treatment.

(2) Formation of Electrodes

Then, a gate electrode 5 is formed. As the electrode material, the onedescribed above can be employed.

To form an electrode film, known various methods may be employed, suchas a vacuum vapor deposition method, a sputtering method, a coatingmethod, a printing method and a sol gel method.

After the film formation, patterning is carried out, as the caserequires to obtain a desired shape. Also for such patterning, knownvarious methods may be employed. For example, a photolithography methodin which patterning and etching (wet etching with an etching liquid, ordry etching by reactive plasma) of a photoresist are combined, aprinting method such as ink jet printing, screen printing, offsetprinting or relief printing, a soft lithography method such as amicrocontact printing method, and a method having a plurality of suchmethods combined, may be used. Further, a pattern may directly beprepared, for example, by irradiating energy rays such as laser orelectron rays to remove the material or to change theelectro-conductivity of the material.

(3) Insulating Layer

Then, an insulator layer 2 is formed. As the insulator material, the onedescribed in the above (3) can be employed.

To form the insulator layer 2, known various methods may be employed.For example, a coating method such as spin coating or blade coating, aprinting method such as screen printing or ink jet printing, a vacuumvapor deposition method, a sputtering method, or a method of forming anoxide film on a metal, such as alumite on aluminum, may be employed.

In an embodiment wherein a semiconductor layer is formed on an insulatorlayer, a prescribed surface treatment may be applied to the insulatorlayer in order to have semiconductor molecules well aligned at theinterface of the two layers. The method for the surface treatment may bethe same as used for the surface treatment of the substrate.

Further, a source electrode 3 and a drain electrode 4 are formed, butthe forming method, etc. may be in accordance with those for the gateelectrode 5.

(4) Semiconductor Layer

Then, an organic semiconductor layer 1 is formed. As the organicsemiconductor material, the one described above can be employed. To formthe semiconductor layer, known various methods may be employed. However,they may be generally classified into a method for forming by a vacuumprocess such as a sputtering method or a vapor deposition method, and amethod for forming by a solution process, such as a coating method or aprinting method.

(5) Vacuum Process

A method of forming an organic semiconductor material into a film by avacuum process to obtain an organic semiconductor layer, will bedescribed in detail. For example, a vacuum vapor deposition method maybe employed wherein the material is put into a crucible or a metal boatand heated in vacuum to evaporate it and to let it deposit on thesubstrate. At that time, the vacuum degree is usually at most 1×10⁻³Torr (1.3×10⁻¹ Pa), preferably at most 1×10⁻⁶ Torr (1.3×10⁻⁴ Pa).Further, depending upon the substrate temperature, the properties of thesemiconductor film, and accordingly, of the device, will change, andaccordingly, the optimum substrate temperature is selected. It isusually within a range of from 0° C. to 200° C. Further, the vapordeposition rate is usually at least 0.001 nm/sec, preferably at least0.01 nm/sec. However, it is usually at most 10 nm/sec, preferably atmost 1 nm/sec. Instead of the method of heating and evaporating thematerial, a sputtering method may be employed wherein accelerated ionsof e.g. argon are impinged to the material target to drive out thematerial atoms and to let them deposit on the substrate.

The organic semiconductor material of the present invention is arelatively low molecular compound. Accordingly, such a vacuum processcan be employed. The vacuum process requires an expensive installationbut has a merit such that the film forming performance is good, and auniform film can readily be obtained.

(6) Solution Process

A method of forming an organic semiconductor material into a film by asolution process thereby to obtain an organic semiconductor layer, willbe described in detail. Firstly, the organic semiconductor material isdissolved in a solvent and coated on a substrate. As the coating method,a coating method such as casting wherein the solution is simply dropped,spin coating, dip coating, blade coating, wire bar coating or spraycoating, a printing method such as ink jet printing, screen printing,offset printing or relief printing, a soft lithography method such as amicrocontact printing method, or a method having a plurality of suchmethods combined, may be employed. Further, as a technique similar tothe coating, a Langmuir•Blodgett method wherein a monomolecular filmformed on a water surface is transferred to and laminated on asubstrate, or a method of interposing liquid crystal or molten liquidbetween a pair of substrates or introducing it between the substrates bya capillary phenomenon, may, for example, be mentioned.

It is advantageous to use the solution process in that an organicelectronic device having a large area can readily be prepared by arelatively inexpensive installation.

A device may also be prepared by dissolving the generalized porphyrincompound of the present invention in a solvent, followed by coating. Insuch a case, the generalized porphyrin compound to be finally used inthe device, may directly be coated, but it is also possible to have ahighly soluble compound (hereinafter referred to as a precursor) coatedand finally converted to a generalized porphyrin compound by the changeof its chemical structure. This is particularly useful to form thematerial hardly soluble in a solvent into a film by a coating method.

As such a precursor, one having the following bicyclo structure may bementioned as a preferred example.

This bicyclo structure changes into a benzene ring by dissociation ofthe ethylene molecule by heating.

The bicyclo structure is sterically bulky and thus is poor incrystallizability. Molecules having this structure have good solubility,and have, in many cases, such a nature that when coated from theirsolution, a low crystalline or amorphous film can readily be obtained.When it changes into a benzene ring by the heating step, it will have amolecular structure having a good planar nature, and thus it changesinto molecules having good crystallizability. Accordingly, by utilizingthe chemical change from such a precursor, it is possible to obtain afilm having a good crystallinity by coating. This heating step may alsohave another purpose such as to distill off the coating solvent.

Particularly, among generalized porphyrin compounds of the presentinvention, a compound so-called a benzoporphyrin, having a benzene ringcondensed to a pyrrole ring, a thiophene ring or a furan ring, can beobtained from one having a bicyclo structure as the precursor, and assuch, it is advantageous to obtain a device by coating.

Further, by the solution process, the semiconductor layer may be madethick by repeating the coating and drying steps as many times asrequired. In a case where a semiconductor film is formed by conversionfrom a precursor, it is possible to form a thick film by lamination byutilizing the difference in solubility between the precursor and thesemiconductor by repeating the coating and conversion to semiconductorsteps.

Further, different film forming methods such as coating and vapordeposition, may be used in combination, or different materials may belaminated by the same or different film forming methods.

In general, it is considered that by the solution process, thefilm-forming performance is not high, and it is difficult to obtain ahighly crystalline organic semiconductor film. However, according tothis method, a highly crystalline organic semiconductor film having goodproperties can be obtained by a simple solution process, such being verydesirable. The film thus formed has a high carrier mobility and hasdesirable characteristics such that the leak current is small, and theON/OFF ratio is high. This method is an excellent method which isapplicable not only to the organic semiconductor material of the presentinvention, but widely to organic semiconductor materials in general.

(7) Post Treatment of the Semiconductor Layer

The organic semiconductor layer thus prepared may be subjected to posttreatment to further improve the characteristics. For example, by heattreatment, it is possible to relax a strain in the film formed duringthe film formation, whereby it is possible to improve the properties orstability. Further, by exposing it to an oxidizing or reducing gas orliquid, such as oxygen or hydrogen, the property change by oxidation orreduction may be induced. This may be utilized, for example, for thepurpose of increasing or decreasing the carrier density in the film.

(8) Doping Treatment

Further, by adding a trace amount of an element, an atomic group, amolecule or a polymer by doping, it is possible to have the propertieschanged to be desirable. For example, oxygen, hydrogen, an acid such ashydrochloric acid, sulfuric acid or sulfonic acid, a Lewis acid such asPF₆, AsF₅ or FeCl₃, a halogen atom such as iodine, or a metal atom suchas sodium or potassium, may, for example, be doped. This can beaccomplished by contacting the semiconductor layer with such a gas, bydipping it in a solution, or by subjecting it to electrochemical dopingtreatment. Such doping may be carried out not only after forming thefilm but also by an addition during the preparation of the material, orin the production process from a solution, by an addition to thesolution or by an addition to the stage of a precursor film. Further, itis also possible to carry out doping by co-vapor depositing the materialto be added during the vapor deposition, by mixing the dopant to theatmosphere during the film formation, or by accelerating ions in vacuumto impinge them to the film.

The effects of such doping may, for example, be a change in theelectroconductivity due to an increase or decrease of the carrierdensity, a change in the polarity of the carrier (p-type, n-type), achange in the Fermi level, etc., and they are commonly used insemiconductor devices. Doping treatment can be likewise utilized for theorganic electronic device of the present invention.

(9) Protective Layer

In the organic electronic device of the present invention, between therespective layers or on the outer surface of the device, another layermay be provided as the case requires. For example, a protective layermay be formed on the semiconductor layer directly or via another layer,whereby the influence of the external atmosphere can be minimized.Further, there is another merit that the electrical characteristics ofthe device can be stabilized. As the material for the protective layer,the one described above may be employed.

To form the protective layer, known various methods may be employed.However, in a case where the protective layer is made of a resin, amethod of coating a resin solution, followed by drying to form a resinfilm, or a method of coating or vapor depositing a resin monomer,followed by polymerization, may, for example, be employed. It is alsopossible to carry out crosslinking treatment after the film formation.In a case where the protective layer is made of an inorganic substance,a forming method by a vacuum process such as a sputtering method or avapor deposition method, or a forming method by a solution processrepresented by a sol gel method, may, for example, be employed.

Now, the present invention will be described in further detail withreference to Examples. However, it should be understood that the presentinvention is by no means restricted to such specific Examples.

PREPRATION EXAMPLE 1

A bicyclo compound (1) was prepared by the following synthesis route.

53.5 ml of thiophenol and 51.25 g of potassium hydroxide was dissolvedin 600 ml of ethanol. To this solution, 19.4 ml ofcis-1,2-dichloroethylene was slowly dropwise added. Then, the mixturewas stirred at room temperature for 30 minutes and further heated andstirred at a temperature of from 80 to 90° C. for 23 hours. The solventwas concentrated under reduced pressure, and water was added thereto,followed by extraction with chloroform. The organic layer was washedwith water and a saturated sodium chloride aqueous solution, dried overanhydrous sodium sulfate and concentrated under reduced pressure toobtain cis-1,2-phenylthioethylene.

This cis-1,2-phenylthioethylene and 750 mg of diphenyl diselenide weredissolved in 100 ml of methylene chloride. This solution was cooled inan ice bath, and 175 ml of a 30% hydrogen peroxide aqueous solution wasslowly added thereto. The mixture was vigorously stirred at roomtemperature overnight, whereupon precipitated crystals were collected byfiltration, dissolved in chloroform, then washed with water, a saturatedsodium carbonate aqueous solution and a saturated sodium chlorideaqueous solution, then dried over anhydrous sodium sulfate andconcentrated under reduced pressure. Further, this product was dissolvedin 500 ml of chloroform, and while cooling the solution in an ice bath,84 g of m-chloroperbenzoate was slowly added, and the mixture wasstirred at room temperature overnight. Precipitated solid was subjectedto filtration by cerite, and the organic layer was washed with water, asaturated sodium carbonate aqueous solution and a saturated sodiumchloride solution, dried over anhydrous sodium sulfate and thenconcentrated under reduced pressure. This solid was rinsed by ethylether to obtain 67.06 g of cis-1,2-diphenylsulfonylethylene (yield:87%). Colorless crystal, mp: 100 to 101° C.

This cis-isomer and a catalytic amount of iodine were dissolved inmethylene chloride, followed by irradiation with sunlight, whereuponprecipitated solid was collected by filtration to obtaintrans-1,2-diphenylsulfonylethylene. Colorless crystals, mp: 219.5° C.

29.33 g of trans-1,2-diphenylsulfonylethylene was dissolved in 200 ml oftoluene, and then, 11.4 ml of 1,3-cyclohexadiene was added, followed bydry distillation for 21 hours and then by recrystallization to obtain35.66 g (yield: 96.5%) of 5,6-diphenylsulfonyl-bicyclo-[2,2,2]oct-2-ene.

7.76 g of this compound was put into a reactor, and after flushing withnitrogen, 50 ml of anhydrous tetrahydrofuran (THF) was added anddissolved. 2.43 ml of ethyl cyanoacetate was added thereto, and thereaction solution was cooled in an ice bath, and 50 ml of a 1M solutionof t-BuOK/THF was slowly dropwise added thereto. Thereafter, thereaction solution was returned to room temperature and stirredovernight. The reaction solution was quenched with 1N hydrochloric acidand extracted with chloroform, followed by washing with water and asaturated sodium chloride aqueous solution. Then, the organic layer wasdried over anhydrous sodium sulfate, concentrated under reduced pressureand purified by silica gel chromatography to obtain 3.49 g (yield:80.4%) of ethyl 4,7-dihydro-4,7-ethano-2H-isoindole-1-carboxylate.Colorless crystals, mp: 129–130° C.

0.109 g of the obtained crystals were dissolved in 15 ml of THF, and0.144 g of LiAlH₄ was dropwise added thereto at 0° C. with stirring,followed by stirring at 0° C. for 2 hours. The reaction solution wasinjected into 25 ml of water and extracted three times with 50 ml ofchloroform. The extracted solutions were put together, and 0.010 g ofp-toluenesulfonic acid was added thereto, followed by stirring at roomtemperature for 12 hours. Then, 0.150 g of p-chloranil was addedthereto, followed by stirring at room temperature for 12 hours. Then,the reaction solution was injected to water. The organic layer wasseparated and washed five times with 250 ml of an aqueous sodiumhydrogencarbonate solution, once with 250 ml of water and 100 ml of asaturated sodium chloride aqueous solution, followed by drying overmagnesium sulfate. The solvent was distilled off, and the residue waspurified by column chromatography (chloroform, alumina) to obtain 0.094g of the desired porphyrin compound (1) containing the bicyclostructure.

The main peak of m/Z=622 (M⁻) was observed by a negative ion mode of theMALDI-TOF mass spectrum.

The results (DTA-TG) of the thermal analysis of this compound are shownin FIG. 4.

Within a temperature range of from 146° C. to 198° C., a decrease inweight and heat generation are observed. This weight reduction (about18%) corresponds to detachment of four ethylene molecules from thebicyclo compound to the change into tetrabenzoporphyrin.

A chloroform solution of the porphyrin compound (1) was dropped on agold-vapor deposited film, and the solvent was dried to form a film. TheIR spectrum of the film is shown in FIG. 5. This film was heated at 210°C. for 2 minutes, and the IR spectrum of the film is shown in FIG. 6. Achange of the IR spectrum reflecting the change in the molecularstructure due to the detachment of the ethylene molecules, was observed,whereby it is evident that by the heating of the film,tetrabenzoporphyrin was formed.

The bicyclo compound (1) was heated at 210° C. for 10 minutes, and themass spectrum thereof was measured by a negative ion mode in the samemanner as for the bicyclo compound, by the MALDI-TOF method, whereby themolecular ion peak of tetrabenzoporphyrin of m/z=510 (M⁻) was observed,whereby the change into tetrabenzoporphyrin by heating was confirmed.Further, the IR spectrum of this heated one, substantially agreed to theIR spectrum after heating, as measured on the above substrate, wherebyit was confirmed that one formed by the heating was tetrabenzoporphyrin.

The chloroform solution of the bicyclo compound (1) was spin-coated on aquartz glass substrate, and the solvent was dried to form a film. Thisfilm was heated at 210° C. for 10 minutes, and the comparison of theultraviolet-visible light absorption spectra of the films before andafter the heating, is shown in FIG. 7. In this Fig. the change from thebicyclo compound to the tetrabenzoporphyrin (690 nm) is observed as anincrease in the intensity and a shift to a long wavelength side, of theQ band in the absorption spectrum of the porphyrin.

PREPARATION EXAMPLE 2

0.02 g of the bicyclo compound (1) of Preparation Example 1 and 0.1 g ofzinc acetate dihydrate were put in a solvent mixture comprising 30 ml ofchloroform and 3 ml of methanol, followed by stirring at roomtemperature for 3 hours. The reaction solution was washed twice with 100ml of water and once with 40 ml of a saturated sodium chloride aqueoussolution. The organic phase was dried over sodium sulfate. The solventwas distilled off, and the obtained solid was recrystallized from asolvent mixture of chloroform and methanol to obtain 0.022 g of a zinccomplex of the bicyclo compound (1). Further, by gel permeationchromatography (Nippon Bunseki Kogyo JAIGEL-1H, 2H, chloroform), onlythe single peak was fractionated and purified.

The mass spectrum was measured, and the molecular peak was confirmed.

PREPRATION EXAMPLE 3

Preparation of 21,23-dithiaporphyrin 5

A dithiaporphyrin compound having the following bicyclo ring structurewas prepared by the following synthesis route.

Here, the starting material diformylthiophene was prepared by the methodreported in Tetrahedron Letters, vol. 43, 8485, (2002).

(1) Preparation of1,3-bis-(dihydroxymethyl)-4,7-dihydro-4,7-ethano-2-benzo[c]thiophene 2

Into a 50 ml flask, diformylthiophene 1 (0.437 g, 2.0 mmol) was put anddissolved in 10 ml of dichloromethane and 10 ml of methanol. The flaskwas cooled to 0° C. and then, NaBH₄ (0.277 g, 6.0 mmol) was added,followed by stirring for 30 minutes. The reaction solution was quenchedwith water. Then, the organic layer was extracted with dichloromethane.The organic layer was washed with water and a saturated sodium chlorideaqueous solution, then dried over sodium sulfate and concentrated. Theobtained oil was crystallized in a refrigerator and then purified byrecrystallization (CHCl₃/hexane) to obtain dihydroxymethylthiophene 2 asthe desired product in a yield of 78%. Appearance: colorless crystals,mp: 143 to 145° C.

(2) Preparation Thiatripyran Diethyl Ester 3

Into a 200 ml flask, dihydroxymethylthiophene 2 (0.888 g, 4.0 mmol) andbicyclopyrrole ethyl ester (1.737 g, 8.0 mmol) were put, and afterflushing the interior of the flask with argon, dissolved in 60 ml ofchloroform. This flask was cooled to 0° C., and 1 ml of TFA was added,followed by stirring for 1 hour and then by refluxing for 5 hours. Thereaction solution was poured into water and quenched. Then, the organiclayer was extracted with chloroform. The organic layer was washed withwater, an aqueous sodium bicarbonate solution and a saturated sodiumchloride aqueous solution and then dried over sodium sulfate andconcentrated. The obtained crude product was washed with a solventmixture of ethyl ether and hexane and then purified by recrystallization(CHCl₃/hexane) to obtain thiatripyran diethyl ester 3 as the desiredproduct in a yield of 90%. Appearance: slightly brown powder (containingsteric isomers), mp: >180° C. (decomposed).

(3) Preparation of Thiatripyran Dicarboxylic Acid 4

Into a 100 ml flask, thiatripyran diethyl ester 3 (0.620 g, 1.0 mmol)was put and dissolved in 10 ml of tetrahydrofuran (THF), 8 ml of ethanoland 12 ml of water. LiOH.H₂O (0.840 g, 20 mmol) was added, followed byrefluxing for 20 hours. The reaction solution was cooled to roomtemperature, and a 1N HCl aqueous solution was slowly added, and the pHof the solution was adjusted to 1. Then, the organic layer was extractedwith ethyl acetate. The organic layer was washed with water and asaturated sodium chloride aqueous solution, then dried over sodiumsulfate and concentrated. The obtained crude product was washed with asolvent mixture of ethyl ether and hexane to obtain thiatripyrandicarboxylic acid as the desired product in a yield of 98%. This productwas used for the next reaction without purification. Appearance: slightbrown powder (containing steric isomers).

(4) Preparation of 21,23-dithiaporphyrin 5

Into a light-shielded 500 ml flask, thiatripyran dicarboxylic acid 4(0.508 g, 0.9 mmol) was put, and after flushing the interior with argon,2.5 ml of TFA was put at room temperature, followed by stirring for 5minutes. 200 ml of dry CH₂Cl₂ was added and then diformylthiophene(0.196 g, 0.9 mmol) was quickly added, followed by stirring at roomtemperature for 16 hours. Then, triethylamine was slowly added toneutralize the solution, and then DDQ (0.227 g, 1.0 mmol) was added,followed by further stirring for 2 hours. The obtained solution waswashed with water, a saturated sodium carbonate aqueous solution and asaturated sodium chloride aqueous solution, then dried over sodiumsulfate and concentrated. The obtained crude crystals were treated bycolumn chromatography and then purified by recrystallization(CH₂Cl₂/MeOH) to obtain dithiaporphyrin 5 as the desired product in ayield of 37%. Appearance: greenish brown solid (containing stericisomers), mp: >130° C. (decomposed). The elemental analysis, NMR andmeasurement of mass spectrum, were carried out to confirm the desiredproduct.

PREPARATION EXAMPLE 4 Preparation of 21-thiaporphyrin

In the same manner as in Preparation Example 3, thiatripyrandicarboxylic acid 4 was prepared. In the same manner as in PreparationExample 3 except that this thiatripyran dicarboxylic acid 4 and apyrrole derivative instead of thiophene were employed, a thiaporphyrincompound having the following bicyclo structure was prepared by thefollowing synthesis route.

Into a light-shielded 500 ml flask, thiatripyran dicarboxylic acid 4(0.508 g, 0.9 mmol) was put, and after flushing the interior with argon,2.5 ml of TFA was put at room temperature, followed by stirring for 5minutes. 200 ml of dry CH₂Cl₂ was added, and then, diformylpyrrole(0.181 g, 0.9 mmol) was quickly added, followed by stirring at roomtemperature for 16 hours. Then, triethylamine was slowly added toneutralize the solution, and then DDQ (0.227 g, 1.0 mmol) was added,followed by stirring for further 2 hours. The obtained solution waswashed with water, a saturated sodium carbonate aqueous solution and asaturated sodium chloride aqueous solution, then dried over sodiumsulfate and concentrated. The crude crystals were treated by columnchromatography (alumina, 50% ethyl acetate/hexane) and then purified byrecrystallization (CH₂Cl₂/MeOH) to obtain thiaporphyrin 6 as the desiredproduct in a yield of 42%. Appearance: greenish purple solid (containingsteric isomers), mp: >130° C. (decomposed). The elemental analysis, NMRand measurement of mass spectrum, were carried out to confirm thedesired product.

EXAMPLE 1

On a N-type silicon substrate (Sb-doped, resistivity: at most 0.02 Ωcm,manufactured by Sumitomo Metals Industries, Ltd.) having 300 nm of anoxide film formed thereon, gold electrodes (source and drain electrodes)having a length (L) of from 2.5 to 50 μm, a width (W) of 250 μm or a gapof 1,000 μm, were formed by photolithography. Further, the oxide film ata position different from these electrodes, was etched with ahydrofluoric acid/ammonium fluoride solution, and to the exposed Siportion, gold was vapor-deposited to form an electrode (gate electrode)to apply a voltage to the silicon substrate.

2 mg of the bicyclo compound (1) obtained in Preparation Example 1 wasdissolved in 1 ml of chloroform, and this solution was dropped betweenthe source and drain electrodes, followed by evaporation of the solvent,and this operation was repeated a few times to obtain a good film. TheX-ray diffraction of this film was observed, whereby no sharp peak wasobserved. Further, this film was observed under a crossed nicolsmicroscope, whereby a dark image over the entire surface was obtained,thus indicating an isotropic film. Accordingly, the obtained film wasfound to be amorphous.

This substrate was heated at 210° C. for 10 minutes. The X-raydiffraction of the obtained film was observed, whereby a sharp peak wasobserved. Further, the film was observed under a crossed nicolsmicroscope, whereby a colored domain structure was observed.Accordingly, the obtained film was found to be crystalline. Thisindicates that the bicyclo compound changed to tetrabenzoporphyrin andbecame crystalline. Further, the obtained film had a low solubility in asolvent and was hardly soluble in an organic solvent.

The characteristics of the field effect transistor thus obtained weremeasured by means of a semiconductor parameter analyzer 4155Cmanufactured by Agilent Technologies. The results of the measurement areshown in FIG. 8.

The operation may be represented as follows, wherein Id is the currentflowing under a voltage Vd applied across the source and the drain, Vgis the voltage applied to the source and the gate, Vt is the thresholdvoltage, Ci is the capacitance per unit area of the insulating film, Lis the distance between the source electrode and the drain electrode, Wis the width, and μ is the mobility of the semiconductor layer.

When Vd<Vg−Vt,

$I_{d} = {\mu\;{{C_{i}\left( \frac{W}{L} \right)}\left\lbrack {{\left( {V_{g} - V_{t}} \right)V_{d}} - \left( \frac{V_{d}^{2}}{2} \right)} \right\rbrack}}$when Vd>Vg,I _(d)=(½)μC _(i)(W/L)(V ₈ −V _(t))²

Thus, the mobility μ is an important parameter of the material governingthe characteristics of the device (transistor), and in order to obtain adevice having high characteristics, a material having high μ isrequired.

Inversely, μ can be obtained from the current-voltage characteristics ofthe device. To obtain μ, the formula (1) or (2) is employed. However,for the mobility μ, there are a few definitions, i.e. an effectivemobility μeff obtained from the slope of Id-Vd at a certain Vg, a fieldeffect mobility μFE obtained from the slope of Id-Vg at a certain Vd,and a saturated mobility μsat obtained from the slope of Id^(1/2)-Vg ofthe saturated current portion of the formula (2). The effective mobilityμeff, the field effect mobility μFE and the saturated mobility μsatshould have the same values in the model obtained by the above formula,and in reality, they become the same value with respect to asemiconductor material whereby ideal FET characteristics can beobtained. However, because of the difference between the real propertiesof the semiconductor material and the model, they may sometimes takedifferent values.

From FIG. 8, the respective mobilities were obtained, whereby theeffective mobility μeff was 1×10⁻³ cm²/Vs, the field effect mobility μFEwas 1.6×10⁻³ cm²/Vs, and the saturated mobility μsat was 0.7×10⁻³cm²/Vs.

EXAMPLE 2

Using chlorobenzene as a solvent, a film of a bicyclo compound wasprepared in the same manner as in Example 1 and converted tobenzoporphyrin by heating.

The characteristics of the field effect transistor thus obtained weremeasured by a semiconductor parameter analyzer 4155C, manufactured byAgilent Technologies. The effective mobility μeff was 1.6×10⁻² cm²/Vs,and the saturated mobility μsat was 1.3×10⁻² cm²/Vs.

EXAMPLE 3

On a slide glass having aluminum vapor-deposited thereon, a solutionhaving oxydianiline and benzophenone tetracarboxylic anhydride dissolvedin dimethylformamide in a molar ratio of 1:1, was spin-coated andheat-treated at 250° C. to prepare a polyimide film having a thicknessof 500 nm. On this film, a film of a bicyclo compound was formed in thesame manner as in Example 1 and converted to benzoporphyrin by heating.

Gold was vapor-deposited thereon through a shadow mask prepared byemploying a tungsten wire having a diameter of 25 μm at the gap portion,to prepare source and drain electrodes having a gap having a width (W)of 250 μm and a length (L) of 25 μm. The characteristics of the fieldeffect transistor thus obtained, were measured by a semiconductorparameter analyzer 4155C, manufactured by Agilent Technologies. Theeffective mobility μeff was 3.7×10⁻² cm²/Vs, and the saturated mobilityμsat was 1.4×10⁻² cm²/Vs.

EXAMPLE 4

Using a zinc complex prepared in Preparation Example 4, FET was preparedin the same manner as in Example 1. The characteristics of this FET weremeasured, whereby the effective mobility μeff was 1.9×10⁻⁴ cm²/Vs, andthe saturated mobility μsat was 1.3×10⁻⁴ cm²/Vs.

EXAMPLE 5

The bicyclo compound (1) obtained in Preparation Example 1 was heated at210° C. for 30 minutes and converted to tetrabenzoporphyrin. Thisproduct was vacuum vapor-deposited on the same electrode substrate as inExample 1 under a vacuum degree of 2×10⁻⁶ Torr (2.6×10⁻³ Pa) to preparea field effect transistor. The relation between the substratetemperature during vacuum deposition and the mobility (the saturatedmobility) of transistor is shown in Table 1. From this relation, it isevident that the mobility differs depending upon the substratetemperature.

TABLE 1 Substrate temperature Saturated mobility μsat Room temperature2.9 × 10⁻⁴ cm²/Vs  80° C. 2.3 × 10⁻⁶ cm²/Vs 150° C. 5.6 × 10⁻⁷ cm²/Vs200° C. 2.8 × 10⁻⁸ cm²/Vs

Further, in FIG. 9, with respect to ones vapor-deposited at atemperatures of 80° C. to 200° C., the X-ray diffraction patterns areshown. From the comparison of these, it is considered that crystal formsare different as between at least 150° C. and at most 80° C., and ineither case, the peak is little, and it is thus considered that the filmis strongly aligned to the substrate. Accordingly, it is considered thatthere was a substantial difference in the observed mobility.

EXAMPLE 6

The benzoporphyrin of Preparation Example 1 was subjected tochloroform/silica gel column chromatography and chloroform/methanolrecrystallization repeatedly to obtain a highly purified product. InPreparation Example 1, the purity at an absorbance at 254 nm by liquidchromatography was 99.0%, whereas with this highly purified product, itwas 99.7%.

A field effect transistor was prepared in the same manner as in Example1 except that using this highly purified product, a precursor film wasprepared by spin coating in a dry nitrogen and heated at 210° C. for 5minutes in nitrogen on a hot plate.

For evaluation, a saturated mobility μsat to be calculated from theplotted inclination of the gate voltage and the square route of thedrain current Id, was obtained based on the relation between the gatevoltage and the current in the saturated region, whereby the saturatedmobility μsat was found to be at least 0.016 cm²/Vs. Further, the ON/OFFratio was obtained from the ratio of the drain current between in thecase of a gate voltage of 0 V and in the case of a gate voltage of −30V, at a drain voltage of −30 V, whereby the ON/OFF ratio was found to beat least 10³, and 10⁵ at best.

FIG. 10 shows the X-ray diffraction patterns of a semiconductor layerobtained in Example 6 and a semiconductor layer prepared by vapordeposition at a substrate temperature of 150° C. in Example 5. The peaksat low angles agree to each other, whereby both appear to be similarcrystals, but the diffraction patterns are substantially different.Therefore, the states of the films such as the alignment, crystallinity,etc. are considered to be different. Accordingly, it is considered thatthe semiconductor layer obtained by coating and heating exhibitsexcellent characteristics.

EXAMPLE 7

On the device prepared in Example 6, a toluene solution of polymethylmethacrylate (PMMA) was spin-coated, followed by drying at 120° C. toform a film of 2 μm.

To this device, and to the device prepared in Example 6, while fixingthe drain voltage at −30 V, the gate voltage was changed from 50 V→−50V→50 V, and the drain current was measured. The results are shown inFIG. 11. It is evident that even in the absence of the PMMA film, theON/OFF ratio is at least 10³ and thus shows good characteristics, but ifthe PMMA film is provided, the hysteresis of the drain current byscanning of the gate voltage is small, and also the ON/OFF ratio isimproved.

EXAMPLE 8

A FET was prepared in the same manner as in Example 1 by employing thedithiaporphyrin prepared in Preparation Example 3. Namely, on asubstrate having electrodes formed in the same manner as in Example 1, aprecursor having the following bicyclo structure was coated and thenheat-treated to prepare a film of tetrabenzodithiaporphyrin. Theelectrical characteristics of the FET device thus obtained weremeasured, whereby the FET characteristics were observed, and thesaturated mobility was 1.1×10⁻⁴ cm²/Vs, and the ON/OFF ratio was 1,000.

EXAMPLE 9

A FET was prepared in the same manner as in Example 1 by employing thethiaporphyrin prepared in Preparation Example 4. Namely, on a substratehaving electrodes formed in the same manner as in Example 1, theprecursor having the following bicyclo structure was coated and thenheat-treated to prepare a film of tetrabenzothiaporphyrin. Theelectrical characteristics of the FET device thus obtained weremeasured, whereby the FET characteristics were observed, and thesaturated mobility was 2.5×10⁻⁵ cm²/Vs, and the ON/OFF ratio was 380.

EXAMPLE 10

A FET was prepared in the same manner as in Example 1 by employing thefollowing zinc complex. Namely, on a substrate having electrodes formedin the same manner as in Example 1, a precursor having the followingbicyclo structure was coated and then heat-treated to prepare asemiconductor film, whereby a field effect transistor was obtained. Theelectrical characteristics of the FET device thus obtained weremeasured, whereby the saturated mobility μsat was 0.7×10⁻⁴ cm²/Vs, andthe effective mobility μeff was 1×10⁻⁴ cm²/Vs.

COMPARATIVE EXAMPLE 1

Fields effect transistors were prepared by employing the generalizedporphyrin compounds represented by the following respective formulas,and their electrical characteristics were evaluated, but in each case,no FET characteristics were observed.

The molecular structures of these generalized porphyrin compounds wereobtained by e.g. the molecular orbital method (such as MOPAC) and themolecular dynamics method (MM2), whereby it was confirmed that atomsconstituting the porphyrin skeleton are present at positions apart atleast 1 Å from the generalized porphyrin ring plane.

According to the present invention, an organic semiconductor material isused for an organic electronic device, whereby it can be produced by arelatively low temperature process, whereby a plastic film can be usedas the substrate, and it is possible to prepare a device which is lightin weight, excellent in flexibility and scarcely breakable. Accordingly,a field effect transistor with a thin film having flexibility, can beprepared, and this can be utilized for a switching element for eachcell, whereby a flexible active matrix liquid crystal display can beprepared, and thus it is widely applicable.

Further, an organic semiconductor material and an organic electronicdevice containing the generalized porphyrin compound of the presentinvention, has a high carrier mobility and stability, and further can beprepared by a simple production process. Further, the field effecttransistor of the present invention has a little leak current and alarge ON/OFF ratio and thus has a merit such that the stability of thefilm and characteristics is high and the useful life is long. Further,the useful temperature range is wide, the film forming property is good,it is applicable to a large area, and it can be prepared at low cost.

1. An organic semiconductor material comprising a compound which has ageneralized porphyrin skeleton and which has a molecular structure suchthat the distance from the generalized porphyrin ring plane to thecenter of each atom forming the generalized porphyrin skeleton, is notmore than 1 Å.
 2. The organic semiconductor material according to claim1, wherein said compound is a compound which has a porphyrin skeletonand which has a molecular structure such that the distance from theporphyrin ring plane to the center of each atom forming the porphyrinskeleton, is not more than 1 Å.
 3. The organic semiconductor materialaccording to claim 1, wherein the compound having a generalizedporphyrin skeleton, has a mobility of at least 1×10⁻⁵ cm²/Vs.
 4. Theorganic semiconductor material according to claim 1, wherein thecompound having a generalized porphyrin skeleton, has a molecular weightof at most 2,000.
 5. The organic semiconductor material according toclaim 1, wherein the compound having a generalized porphyrin skeleton,is a benzoporphyrin.
 6. The organic semiconductor material according toclaim 1, wherein the compound having a generalized porphyrin skeleton,is one obtained by conversion from a precursor.
 7. The organicsemiconductor material according to claim 1, wherein the compound havinga generalized porphyrin skeleton, is a compound containing no metal. 8.An organic electronic device comprising a semiconductor layer and atleast two electrodes, wherein the semiconductor layer contains theorganic semiconductor material as defined in claim
 1. 9. The organicelectronic device according to claim 8, wherein a protective layer isformed, directly or via another layer, on the semiconductor layer. 10.The organic electronic device according to claim 8, wherein the organicelectronic device is a switching device.
 11. The organic electronicdevice according to claim 8, wherein the organic electronic device is afield effect transistor.
 12. The organic semiconductor materialaccording to claim 1, wherein the compound which has a generalizedporphyrin skeleton is a copper-containing compound.
 13. An organicsemiconductor material comprising a compound which has a generalizedporphyrin skeleton and which has a mobility of at least 1×10⁻⁵ cm²/Vs,wherein the compound having a generalized porphyrin skeleton, is abenzoporphyrin.
 14. The organic semiconductor material according toclaim 13, wherein the compound having a generalized porphyrin skeleton,has a molecular weight of at most 2,000.
 15. The organic semiconductormaterial according to claim 13, wherein the compound having ageneralized porphyrin skeleton, is one obtained by conversion from aprecursor.
 16. The organic semiconductor material according to claim 13,wherein the compound having a generalized porphyrin skeleton, is acompound containing no metal.
 17. An organic electronic devicecomprising a semiconductor layer and at least two electrodes, whereinthe semiconductor layer contains the organic semiconductor material asdefined in claim
 13. 18. The organic electronic device according toclaim 17, wherein a protective layer is formed, directly or via anotherlayer, on the semiconductor layer.
 19. The organic electronic deviceaccording to claim 17, wherein the organic electronic device is aswitching device.
 20. The organic electronic device according to claim17, wherein the organic electronic device is a field effect transistor.21. The organic semiconductor material according to claim 13, whereinthe compound which has a generalized porphyrin skeleton is acopper-containing compound.
 22. An organic semiconductor materialcomprising a compound which contains a structure represented by thefollowing formula (A):

wherein n is an integer of from 4 to 20, each of X¹ to X^(n) which areindependent of one another, is a direct bond or a connecting group whichis a C₁₋₃ linear unsaturated hydrocarbon group, wherein said C₁₋₃ linearunsaturated hydrocarbon group may be substituted with a substituentgroup selected from the group consisting of a linear alkyl group, alinear alkoxy group, a linear alkylthio group, an ester of a carboxylgroup with a C₁₋₁₀ linear alcohol, and a halogen atom, and wherein analkyl moiety of such a substituent may be further substituted with ahalogen atom, rings containing Y¹ to y^(n), wherein each of Y¹ to Y^(n)are independent of one another, is a π-conjugated single ring ofhydrocarbon ring or heterocyclic ring, and each of Y¹ to Y^(n) which areindependent of one another, may be condensed with another hydrocarbonring or heterocyclic ring to form a condensed ring, each of the ringscontaining Y¹ to Y^(n) is an aromatic ring, which may be substituted bywith a substituent group selected from the group consisting of ahydroxyl group, a C₁₋₀ alkyl group, an alkoxy group, a mercapto group,an acyl group, an ester of a carboxyl group with a C₁₋₁₀ alcohol, aformyl group, a carbamoyl group, a halogen atom, an amino group, anamino group substituted by a C₁₋₁₀ alkyl group, and a nitro group, andwherein an alkyl moiety of such a substituent may be further substitutedwith a halogen atom.
 23. The organic semiconductor material according toclaim 22, wherein in the formula (A), each of X¹ to X^(n) which areindependent of one another, is unsubstituted or has a substituentcomposed of a single atom such as a halogen atom.
 24. The organicsemiconductor material according to claim 22, wherein in the formula(A), each of the rings containing Y¹ to Y^(n), which are independent ofone another, is unsubstituted or has a substituent composed of a singleatom such as a halogen atom.
 25. The organic semiconductor materialaccording to claim 22, wherein the molecular weight of the compound isat most 2,000.
 26. The organic semiconductor material according to claim22, wherein the compound is one obtained by conversion from itsprecursor.
 27. The organic semiconductor material according to claim 22,wherein the compound is a compound containing no metal.
 28. An organicelectronic device comprising a semiconductor layer and at least twoelectrodes, wherein the semiconductor layer contains the organicsemiconductor material as defined in claim
 22. 29. The organicelectronic device according to claim 28, wherein a protective layer isformed, directly or via another layer, on the semiconductor layer. 30.The organic electronic device according to claim 28, wherein the organicelectronic device is a switching device.
 31. The organic electronicdevice according to claim 28, wherein the organic electronic device is afield effect transistor.
 32. The organic semiconductor materialaccording to claim 22, wherein the compound which has a generalizedporphyrin skeleton is a copper-containing compound.